Hovering Eristalis nemorum males  (View complete paper)

animation10medium_090831_1656_mnvr

Female on an oscillating flower

In windy conditions a male may hover above a female sitting on an oscillating flower. Oscillations with frequency between 1 and 2 Hz have been measured in this way. The male is delayed with respect to the female.

More information about the delay.

   

animsmall_mnmnvr_090819_1618D8

Wobbling

When the female is not moving too much the hovering male is performing a rolling oscillation about the body axis combined with a horizontal oscillation perpendicular to the body axis. This movement will be called wobbling. The frequency of this oscillation is  between 5 Hz  and 9 Hz. Sometimes two males are wobbling above one female. See animation. The animation is 6X retarded.

 

   
Animation_small_090704_1504AThe fixation point
A male hovering above a female should be able to detect the position of the female accurately. The question remains at which point of the female the male is looking to stabilize its position. This point will be called the fixation point here. Information about the fixation point may be obtained from tracks with a rotating female. The animated picture below is derived from a film. Here the female is rotating 90 degrees from Start to Finish, the male remains positioned above the thorax of the female.

Read more: The fixation point

   

Model for position control 

The excellent following behaviour of  Eristalis nemorum males is suggesting an innate fast and accurate servo control system. The complete system is very complex, including eyes, neurons in different layers and the motor control of the wings. However a largely simplified model may be of use to gain more insight and to be able to relate the experiments.

Model_model

More information about the model

   

Materials and methods

The hovering flies have been filmed near Sint-Michielsgestel, the Netherlands, from April until August 2009.  The camera is a Casio EX-F1. The camera has been used to film in HD with 30 frames per second and in a high speed mode with 300 frames per second.

Information Materials and methods

   

Three males above one female.

   

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